The eastern cities of Kalmunai, Chavalakade and Samanthurai will be under a daily curfew from 8:45 p.m. to 4 a.m. until further notice, police said.

Authorities announced the curfew after security forces were involved in a shootout and seized bomb-making equipment during raids those cities.

A cache of explosives was seized from a house in Samanthurai, following a raid on intelligence information, police said. Security forces also found ISIS uniforms, flags, 150 sticks of explosive Gelignite, 100,000 ball bearings and a drone camera.

Three explosions were reported in nearby Kalmunai. Security forces exchanged fire during a security operation in the Sainda-Marudu area of the city, police said.

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The raids came after the coordinated attacks on Easter Sunday, which killed 253 people, including many worshipers attending Easter Mass services.

National Tawheed Jamath (NTJ), a local extremist group, has been blamed for the bombings, but has not claimed the attacks. ISIS claimed responsibility, but a link between the attackers and the terror group has not been proven.

A video released by ISIS showed eight men purported to be the Sri Lankan attackers.

A news agency linked to ISIS released a video of the purported attackers, which showed them standing in front of a black ISIS banner.

Sri Lankan authorities have been attempting attempting root out any "sleeper" cells who could initiate another round of attacks, Prime Minister Ranil Wickremesinghe told CNN on Thursday.

On Friday, Sri Lanka's President announced a "major search operation" in Sri Lanka.

"Every household in the country will be checked," President Maithripala Sirisena told a press conference according to a statement. "The lists of permanent residents of every house will be established to ensure no unknown persons could live anywhere."

The heightened tensions have put Sri Lankans on edge.

Catholic Sunday masses have been suspended "until further notice" in Sri Lanka, the Archbishop of Colombo Cardinal Malcolm Ranjith announced on Friday. He said the move will ensure the safety of the worshipers, and that the church "will try to introduce some services" once better security was in place.

The government urged Muslims to stay at home for Friday prayers, and many mosques were closed. However, some mosques defied the call, opening for the midday prayers.

Both Christianity and Islam are minority religions in Sri Lanka, each accounting for under 10% of the total population. The vast majority of Sri Lankans identify as Buddhist.